The circadian rhythm in the urinary excretion of free epinephrine, norepinephrine and dopamine was studied in 60 elderly men and 83 women, 77 +/- 8 years of age, in a total of 260 24-hour profiles and in 63 boys and 81 girls, 11 +/- 1.5 years of age, in 144 24-hour profiles. The circadian mesor of all these compounds was increased in the children over that in the elderly subjects while the acrophase remained unchanged in spite of a phase shift of the acrophase of the urine excretion of the elderly in the night hours. The differences in functional state of the sympathetic and adreno-medullary function (and/or response) between children and elderly subjects may have clinical implications.